Why Waist Size Matters for Your Metabolic Health

Two people can weigh exactly the same but have very different health risks — and the difference is often in their waistlines. A tape measure around your middle can reveal hidden fat that quietly disrupts blood sugar control and drives metabolic disease. This type of belly fat isn’t just stored energy — it’s biologically active and closely linked to insulin resistance, diabetes, and heart disease.

Here we describe why waist circumference is a key marker of metabolic health, and what you can do to reduce the health risks associated with this measure.

Visceral Fat: The Hidden Danger

Not all body fat is the same. Fat which lies just under your skin, called subcutaneous fat, is soft and pinchable and not harmful. Whereas the fat that sits deep within your belly, wrapped around organs, called visceral adipose tissue, is strongly linked to diabetes, heart disease and stroke. This fat is metabolically active:

• It releases free fatty acids directly into the liver

• It pumps out inflammatory chemicals

• These changes interfere with how insulin works in your body

That makes visceral fat a strong driver of insulin resistance — a state where your body’s cells don’t respond well to insulin, so your pancreas has to work harder to control blood sugar. Over time, this can lead to type 2 diabetes and other metabolic diseases.

Importantly, waist circumference is closely tied to visceral fat levels, even when BMI (body mass index) might be “normal.” In fact, waist measurement often predicts insulin resistance and diabetes risk better than BMI does.

Waist Size and Disease Risk

Insulin Resistance

Studies show that as waist circumference goes up, so does insulin resistance, even in people with similar BMI. That’s because belly fat is more biologically active and harmful than fat in other areas.

Type 2 Diabetes

Long-term data indicate that increases in waist size are strongly associated with developing type 2 diabetes — even after adjusting for weight gain and other risk factors.

Metabolic Syndrome

Metabolic syndrome is a cluster of risk factors — high blood sugar, high blood pressure, elevated triglycerides, low HDL (“good”) cholesterol — that together raise heart and diabetes risk. Waist circumference is often the first component to become abnormal and helps flag people who may have the full syndrome.

How to Measure Your Waist Size Properly

Measuring your waist circumference can provide a useful indicator of your metabolic health. This can be done by measuring your waist alone, or by calculating your waist to height ratio.

Waist Circumference

To measure your waist:

1. Take your waist measurement in the morning just after you get up, after you have emptied your bladder, but before you have anything to eat or drink

2. Find the spot between the bottom of your ribs and the the top of your hips as shown in the diagram below

3. Place tape measure half way between these points, just above the belly button

4. The tape should be pulled tight but not digging into your skin

5. Breathe out naturally and take your measurement

   
   

From NHS: How to measure your waist to height ratio

Typical cut-offs used in clinical guidance are roughly:

• Women: >35 inches (≈88 cm)

• Men: >40 inches (≈102 cm)

  
  

  People above these levels are often at increased metabolic risk.

Waist-to-Height Ratio (WHtR)

Another useful metric is waist-to-height ratio: divide your waist circumference by your height. For example, a 170 cm tall person with an 85 cm waist has a ratio of 0.5.

• A WHtR of around 0.5 or lower is generally considered healthier.

• Higher WHtR values are linked to more risk of metabolic syndrome and diabetes in adults with type 2 diabetes.

WHtR has some advantages over waist alone because it adjusts for the fact that taller people naturally have larger waists — making it a more consistent predictor of risk across different body sizes.

The NHS has a short video to explain how to measure both your waist and your waist to height ratio - which you can see here.

From NHS: How to measure your waist to height ratio

How a Low-Carbohydrate Way of Eating Can Support Metabolic Health

A low-carbohydrate diet focuses on reducing foods that quickly raise blood sugar — such as refined grains, sugary foods, and sweetened drinks — and replacing them with protein, healthy fats, and fibre-rich vegetables.

For many people, this approach can be especially helpful for improving insulin resistance and reducing belly fat.

Less Sugar Spikes = Less Insulin Demand

Carbohydrates are the main nutrient that raises blood glucose. When carb intake is high, the body must release more insulin to keep blood sugar under control. Over time, repeated high insulin demands can worsen insulin resistance.

Lower-carb eating reduces how often and how high blood sugar rises, which:

• Lowers insulin levels

• Improves insulin sensitivity

• Reduces fat storage, especially in the abdomen

Clinical trials consistently show that low-carbohydrate diets improve blood glucose control in people with insulin resistance and type 2 diabetes, often more quickly than low-fat diets.

Visceral Fat and Waist Size Is Especially Sensitive to Carb Reduction

Visceral fat (the deep belly fat linked to metabolic disease) responds particularly well to reductions in insulin levels.

When insulin is lower:

• Fat breakdown increases

• Liver fat decreases

• Waist circumference often shrinks even before large weight loss occurs.

Studies show that low-carb diets can reduce waist circumference and visceral fat more than calorie-matched higher-carb diets, even when total weight loss is similar.

Improved Triglycerides and HDL (“Good”) Cholesterol

Metabolic syndrome often includes:

• High triglycerides

• Low HDL cholesterol

• Fatty liver

Low-carbohydrate diets reliably:

• Lower triglycerides

• Raise HDL cholesterol

• Reduce liver fat

These changes are strongly linked to reduced cardiovascular and diabetes risk.

Natural Appetite Control and Weight Loss

Protein and fat are more filling than refined carbohydrates. Many people naturally eat fewer calories on a low-carb diet without counting calories, which supports sustainable weight loss and reductions in waist size.

This is important because even 5–10% weight loss can significantly improve insulin resistance and metabolic health — especially when belly fat is reduced.

What Low-Carb Eating Looks Like (in Practice)

A metabolically healthy and nutritionally-dense low-carb plate usually includes:

• Plenty of non-starchy vegetables (leafy greens, broccoli, peppers) and smaller quantities of fruit, such as berries

• Protein (eggs, fish, poultry, meat, tofu, dairy)

• Healthy fats (olive oil, avocado, nuts, dairy)

• Optional whole-food carbs in smaller amounts (legumes, whole grains)

It excludes refined carbs, such as white starchy foods, such as white bread, pasta, rice, sweets and sugary drinks

Is Low-Carb for Everyone?

Low-carbohydrate diets are particularly helpful for people with:

• Insulin resistance

• Type 2 diabetes or pre-diabetes

• Central (abdominal) obesity

• Metabolic syndrome

The best diet is one that is nutritionally complete, enjoyable, and sustainable and some people do well with moderate carbs rather than very low carbs — the key is minimising refined sugars and ultra-processed foods while focusing on whole foods.

Final thoughts

Reducing waist size isn’t about aesthetics — it’s about improving how your body handles energy, sugar, and fat. For many people, a low-carbohydrate way of eating is a powerful tool to shrink visceral fat, lower insulin resistance, and restore metabolic health.